This invention is directed to a seal for a pouch packaging machine. The seal includes first and second seal bars each having a sealing surface thereon. The sealing surfaces on each of the seal bars is an undulating convoluted surface having ridges and grooves. The radius of curvature the grooves is different than the radius of curvature of the ridges.
Many commodities are packaged on form, fill and seal packaging machines. Packaging pouches are formed on these machines from rolls of polymeric and metal foil films or combinations of the same. The pouches are formed, filled, sealed and then disconnected from an advancing stream of pouches being formed on the packaging machine.
In forming these pouches irrespective of the particular packaging film use for a particular pouch, parallel side seams are made between front and back films. These side seams form the sides of individual pouches. Next cross seams perpendicular to the side seams are formed between the front and back films. Each individual cross seam is severed to form a top seam in a bottom most pouch and a bottom seam in the pouch immediately above it on the machine.
The packaging films utilized on form, fill and seal packaging machines to form pouches generally are multilayered films. These packaging films can have anywhere from two to eleven or twelve individual layers. The individual layers of the packaging film are formed of various materials to achieve various packaging results. The materials can include metallic foil films and various polymeric films. Typical polymeric films include polyethylene, polypropylene and nylon films. Typical metal foil films include aluminum foil film.
Typically one or more of the layers of the film that will form the inside of a pouch is engineered by the film manufacturer such that it will soften and flow when subjected to heat and pressure. Both the side seals and the cross seals of a form, fill and seal pouch packaging machine heat and pressurize a front and back film together to adhere the corresponding films to one another. Typically during the heat and pressurization by the seals, the interior layers of the packaging film soften and flow such that they adhere to one another to seal the front and back films together to form a pouch.
To augment the seal between the front and back films, typically the sealing surfaces of the seal bars, whether they be side seals or cross seals are knurled with a "saw tooth" or "square wave" pattern. This stretches the films about the area in which they are sealed together. This stretching increases the surface area of the seal between the films and to some extent mechanically interlocks the front and back films to each other.
In pouches that are designed to have permanent seals, the knurls formed utilizing a knurled sealing surface are normally elongated in a direction parallel to the edge of the pouch that is being sealed such that the mechanical impressions incorporated onto the pouch by the knurled sealing surfaces run parallel with the edge of the pouch. This provides additional strength to the seal by inhibiting tearing of the seal perpendicular to the parallel knurled surface left in the pouch by the seal. Since a perpendicular tear must go across each of the knurls or furls formed on the sides of the pouch, this strengthens the sides of the pouch.
While the presently utilized saw tooth or square wave knurl patterns utilized on the sealing surfaces of the seal bars for pouch packaging machines contributes to increasing the strength of the final seal formed on the pouch, these knurled surfaces are not without their problems.
Especially with metal foil films saw tooth or square wave sealing surfaces tend to fracture the films during sealing. The fractures typically occur along the angular areas of these sealing surfaces because maximum stress of the films occurs at these areas. This stress can lead directly to film fracture.
Additionally, the films tend to stick to the seals about angular areas. This requires the use of a Teflon blanket or other non stick blanket over the sealing surfaces of the seals to prevent sticking of the packaging film to the sealing surfaces.